A, The body and frontal horn of the right lateral ventricle have been exposed through an incision in the anterior part of the corpus callosum. The inset on the upper left shows the head position, scalp incision (solid line) and bone flap (broken line). The bone flap extends across the superior sagittal sinus. An alternative would be to use a Souttar incision and to have the bone flap extend only to the lateral edge of the superior sagittal sinus. B, Sites of incisions used to reach lesions in the third ventricl E, (No. 1) the foramen of Monro may be enlarged by incising the ipsilateral column of the fornix, at the anterosuperior margin of the foramen of Monro; (No. 2) the transforniceal approach is completed using an incision along the body of the fornix in the midline; and (No. 3) the transchoroidal approach is completed by opening the choroidal fissure by incising along the tenia fornicis. C, The transchoroidal approach is completed by incision along the tenia fornicis rather than the tenia choroidea, also referred to as the tenia thalami, because more veins and arteries pass through the tenia choroidea than the tenia fornicis. The internal cerebral veins course in the roof of the third ventricle. (Images courtesy of AL Rhoton, Jr.)